Summary: Ok, I don't know how many PCs I've built over the years (beginning with the first PCs). I never had this kind of problem before... I could not get the onboard Ethernet to work under Windows 7, Windows XP or Windows 2000. The OS kept saying that the cable was unplugged. I tried other cables, other connections (both worked with other PCs), but nothing worked. So, I RMA's the board (many thanks, Amazon). I got my replacement board and tried again. Same problem.